viper_za Posted November 16, 2015 Share Posted November 16, 2015 I finally had some time to install my 3 Panels on the roof over the weekend. 3x ReneSola Virtus II 300W panels connected in series Spec of the panels Maximum Power (Pmax) : 300WPower Tolerance : 0 ~ +5WModule Efficiency : 15.5%Maximum Power Current (Imp) : 8.20AMaximum Power Voltage (VMP) : 36.6VShort Circuit Current (Isc) : 8.69AOpen Circuit Voltage (Voc) : 44.8V The panels are not connected to anything yet except the combiner box so far. Tested with the multimeter and got the following readings yesterday when we had some clear skies with only a cloud now and then. 8:30 AM: 125V and 5.58A 11:30 AM: 125.8V and 9.5A (This scared and impressed me with the multimeter only being rated to 10A) After this i just measured voltage every now and then mostly at around the 121-126v mark too scared i blow my multimeter on amps. What I am wondering is should I not get close to 3x Voc (44.8 x 3 = 134.4V) on clear skies? Thanks for any feedback Quote Link to comment Share on other sites More sharing options...
___ Posted November 16, 2015 Share Posted November 16, 2015 I think temperature is the defining factor here. On a cold morning with bright sunshine you get these insane open circuit voltages. The Voc quoted on the panel is likely such an extreme value that you might never see in this part of the world :-) Quote Link to comment Share on other sites More sharing options...
Chris Hobson Posted November 16, 2015 Share Posted November 16, 2015 For every 1 oC rise above 25oC each panels will lose 0.13V VOC (loss on the string 0.39V) . On a hot day your panels could be anything between 50 - 70 oC. This is important in winter as those 3 panel in series could potentially have a VOC of 146.4 V (@ -5 oC). It is unlikely but it is something to bear in mind when looking at your MPPT's max voltage. Quote Link to comment Share on other sites More sharing options...
viper_za Posted November 16, 2015 Author Share Posted November 16, 2015 Thanks Chris and Plonkster I was just a bit worried it might be a connection issue but then I suppose I should not have seen the 9.5A reading if it was. Cant wait to get the system up and running now just need to get my battries. Quote Link to comment Share on other sites More sharing options...
viper_za Posted November 16, 2015 Author Share Posted November 16, 2015 For every 1 oC rise above 25oC each panels will lose 0.13V VOC (loss on the string 0.39V) . On a hot day your panels could be anything between 50 - 70 oC. This is important in winter as those 3 panel in series could potentially have a VOC of 146.4 V (@ -5 oC). It is unlikely but it is something to bear in mind when looking at your MPPT's max voltage. These are the Axpert Voltages MPPT Range @ Operating Voltage: 60VDC ~115VDC Maximum PV Array Open Circuit Voltage: 145 VDCIf I workout for the string according to spec VMP: 36.6 x 3 = 109.8V VOC: 44.8 x 3 = 134.4V Live in Pretoria and almost never see -temps. In the range but just, should I be worried about damage to the inverter? Quote Link to comment Share on other sites More sharing options...
Chris Hobson Posted November 16, 2015 Share Posted November 16, 2015 Live in Pretoria and almost never see -temps. In the range but just, should I be worried about damage to the inverter? It is unlikely. At 0oC your winter VOC max would be about 145V. However you would need there to be no draw and below freezing and have an irradiance of 1000W/m2. Early in the morning when it is cold, and your are at risk, your batteries should accept charge (so there would be a draw) and you unlikely to have 1000W/m2 at 8 in the morning. My winter VOC max is about 128V DC. The highest I have seen is about 109 oC. There is a risk your panels could exceed 145V DC but I think that risk is small. One could switch off your PV input if you are expecting extreme cold. I have a DC circuit breaker in the house where I can isolate the PV input and measure the voltage without having to step outside and be exposed to the elements. Mark 1 Quote Link to comment Share on other sites More sharing options...
viper_za Posted November 16, 2015 Author Share Posted November 16, 2015 It is unlikely. At 0oC your winter VOC max would be about 145V. However you would need there to be no draw and below freezing and have an irradiance of 1000W/m2. Early in the morning when it is cold, and your are at risk, your batteries should accept charge (so there would be a draw) and you unlikely to have 1000W/m2 at 8 in the morning. My winter VOC max is about 128V DC. The highest I have seen is about 109 oC. There is a risk your panels could exceed 145V DC but I think that risk is small. One could switch off your PV input if you are expecting extreme cold. I have a DC circuit breaker in the house where I can isolate the PV input and measure the voltage without having to step outside and be exposed to the elements. Thanks Chris, also have the combiner in the house with a breaker for the string for just incase Chris Hobson 1 Quote Link to comment Share on other sites More sharing options...
Chris Hobson Posted November 16, 2015 Share Posted November 16, 2015 Thanks Chris, also have the combiner in the house with a breaker for the string for just incase My combiner is outside and have 17 m of 25mm2 armoured cable running from the combiner box into the house. 40 A DC circuit breaker between armoured cable and the inverter. The thing with safety isolators is that you probably never use them but there comes a day, if you did not install them, that you wished you had installed them. Regie 1 Quote Link to comment Share on other sites More sharing options...
Mark Posted January 10, 2016 Share Posted January 10, 2016 Max PV today has so far reached 736W (of Panel Max of 600W (2x300)) 2x ReneSola Virtus II 300W Thats 22.6% better than spec. Temp is around 25 deg with scattered cloud. Nice - but does raise issues around fully populating the inverter (Axpert 5/48V) with 3000W of panels... (could get 3650W)?? Regards Mark Quote Link to comment Share on other sites More sharing options...
Chris Hobson Posted January 10, 2016 Share Posted January 10, 2016 Max PV today has so far reached 736W (of Panel Max of 600W (2x300)) 2x ReneSola Virtus II 300W Thats 22.6% better than spec. Temp is around 25 deg with scattered cloud. Nice - but does raise issues around fully populating the inverter (Axpert 5/48V) with 3000W of panels... (could get 3650W)?? Regards Mark As long as you do not exceed the 115 VDC of the MPPT (inverter max 145 VDC) you should be fine. The inverter will not use more than 3kW even if you produce more than this. Mark 1 Quote Link to comment Share on other sites More sharing options...
Mark Posted January 28, 2016 Share Posted January 28, 2016 Max PV today has so far reached 736W (of Panel Max of 600W (2x300)) 2x ReneSola Virtus II 300W Thats 22.6% better than spec. Temp is around 25 deg with scattered cloud. Nice - but does raise issues around fully populating the inverter (Axpert 5/48V) with 3000W of panels... (could get 3650W)?? Regards Mark Ok today I achieved my MaxPV so far...778W (129%) off my 600W pf panels Scattered cloud and about around 26% Amazed... Quote Link to comment Share on other sites More sharing options...
___ Posted January 28, 2016 Share Posted January 28, 2016 You can't really measure efficiency without also measuring insolation. Panels are rated at a standard 1000w per square meter, but sometimes the sun does better than that, especially if you have clouds to reflect some light off. I've also recorded 20% above rating on such days. Mostly though... It's hotazel and they make maybe 90% of their capacity. Sent from my GT-I9195 using Tapatalk Quote Link to comment Share on other sites More sharing options...
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